Re: [Haskell-cafe] testing for exceptions

Good clarification. Cheers, Darren On Nov 1, 2015 01:09, "Erik Hesselink" wrote:

I think you misinterpreted that answer. As far as I'm aware, `error` (except in its type) is no less reasonable than other exceptions, and you can catch it in IO. So as long as you run a test in IO, you can test for the call to `error` (as Joachim showed in another reply).

Regards,

Erik

On 31 October 2015 at 11:40, Darren Grant wrote:

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Unfrotunately the answer to this is not simple:

http://stackoverflow.com/questions/4243117/how-to-catch-and-ignore-a-call-to...

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'error' more or less terminates the program in an unreasonable way.

It would be preferable for f2 to result in a type that can contain the

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result to be parsed.

Cheers, Darren

On Oct 31, 2015 21:16, "Roelof Wobben" wrote:

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Hello,

I have made this exercise which can be found at the Craft of Functional Programming book.

-- exercise 32

-- Suppose we have to raise 2 to the power n. If n is even, 2*m say,

error then

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...

-- 2n = 22*m = (2m)2 -- If n is odd, 2*m+l say, then -- 2n = 22*m+l = (2n)2*2 -- Give a recursive function to compute 2n which uses these insights.

f2 :: Integer -> Integer f2 n | n < 0 = error "This will only run for positive numbers" | n == 0 = 1 | even n = f2 ( n `div` 2) ^ 2 | odd n = (f2 ( n `div` 2) ^ 2) * 2

Now I have to make Hunit tests for it,

But is there a way I can test if the error message is shown when a negative number is being used ?

Roelof

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